Thin-film magnetoresistance sensing element, combination thereof, and electronic device coupled to the combination

ABSTRACT

A thin film magnetoresistive sensor for detecting a magnetic field components perpendicular and parallel to the plane of the sensor substrate is disclosed. The sensing element comprises a free layer, a reference layer, and a spacer layer between the free layer and the reference layer. The easy-axis magnetization inherent to the material of the free layer is arranged to be perpendicular to the plane of the sensor substrate. The magnetization direction of the reference layer is confined to a direction parallel to the substrate plane. The reference layer consists of a ferromagnetic layer exchange coupled to an antiferromagnetic layer, or consists of a ferromagnetic layer having a higher coercive force than that of the free layer. The spacer layer is composed of an insulating material or a conductive material. The magnetoresistive sensor further includes an array of aforementioned sensing elements coupled to an electronic device to provide three-axis sensing.

CROSS-REFERENCE TO A RELATED APPLICATIONS

This application is a 35 U.S.C. §371 national phase application ofPCT/CN2011/085090, filed on Dec. 30, 2011, which claims priorities to aChinese Patent Application No. 201110141226.X, filed on May. 27, 2011,and a Chinese Patent Application No. 201110002406.X, filed on Jan. 7.2011 incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to the use of a series of magnetic tunneljunction (MTJ, Magnetic Tunnel Junction) sensing elements in a vectormagnetic field measuring system.

BACKGROUND ART

Vector magnetic sensors have become increasingly popular for use aselectronic compasses in consumer devices such as cellular phones andautomobile navigation systems, and for various applications involvingpositioning and measurement. These devices need to consume little powerand can be produced at low cost and in high volume for consumerelectronics.

There are various means by which the magnetic signal could be detectedfor a vector magnetic sensor application, and of these, there are manymagnetic sensing technologies that can be integrated into asemiconductor chip. These include Hall Effect Sensors ormagnetoresistive sensors including anisotropic magnetoresistance (AMR,Anisotropic Magnetoresistance) and giant magnetoresistance (GMR, GiantMagnetoresistance). Hall Effect devices are comparatively expensive andlacking in resolution. They are generally sensitive to fields orientedperpendicular to the plane of the substrate onto which they arefabricated. AMR and GMR devices although they are relativelyhigh-resolution devices, suffer from low signal amplitude and requirecareful attention to be paid to back-end electronics design, whichincreases system complexity and size and therefore increases cost. AMRand GMR sensors are generally sensitive to fields parallel to the planeof the substrate onto which they are deposited.

MTJ sensors detect the magnetic field through the use of the tunnelingmagnetoresistance (TMR, Tunneling Magnetoresistance) effect, offer smallsize, high resolution, and large signal amplitude. These features can beused to simplify electronics design, thereby lowering total system cost.Like AMR and GMR sensors, MTJ sensors are sensitive to fields parallelto the plane of the substrate onto which they are fabricated.

As with most semiconductor devices, the best means to achieve the lowcost and mass production demands is to build the device on a singlesemiconductor substrate. Unfortunately, it is not an easy task to builda three axis vector magnetometer on a single chip as most of the commonsensors only detect parallel or perpendicular field components. To solvethis problem, two or more substrates are often aligned at right anglesto each other, and then packaged together, but this unfortunatelyincreases cost and size.

There are various techniques that have been disclosed to build two-axissensors using all of the above mentioned sensing devices. Unfortunately,these techniques cannot measure the magnetic field componentperpendicular to the plane of the substrate. Hall Effect devices havebeen built that provide all three axes through the use of permeableshields and sometimes through the use of a van der Pauw like techniquefor the in-plane components, but these devices are relatively high powerand low sensitivity.

Another technique that has been proposed is to combine sensors thatdetect perpendicular components with those that detect parallelcomponents, such as Hall Effect sensors with AMR, GMR, or MTJ sensors,but the difference in sensitivity, and possibly process incompatibility,makes this an unattractive solution.

SUMMARY OF THE INVENTION

The present invention discloses a method for making a MTJ sensor that issensitive to fields applied perpendicular to the plane of the sensorsubstrate for use in a single chip integrated vector magnetometersystem.

One aspect of the present invention provides a thin-filmmagnetoresistive sensor element for detecting a magnetic field componentperpendicular to the plane of the. The sensing element includes afreelayer and a reference layer, which are separated by a spacer layer.The inherent easy-axis of said freelayer material is perpendicular toits plane of the substrate, but the magnetization of the freelayer isconstrained to the direction parallel to the substrate plane. Thedirection of magnetization of the reference layer is coupled to anantiferromagnetic layer, or the reference layer is comprised of aferromagnetic material with higher coercivity than the freelayerferromagnetic material. The spacer layer may be made from an insulatingmaterial or a conductive material.

Another aspect of the present invention is to provide a plurality ofsaid sensing elements, deposited onto the same substrate, wherein saidsensing elements are patterned into a plurality of shapes, he sensingelements may inclined along two or more axes such that a plurality ofsensing elements with different sensitivity to the applied magneticfield are formed.

A third aspect of the present invention is to provide a combination ofsaid sensing element s with an electronic device used for thedeconvolution of two or three orthogonal magnetic field components.

A fourth aspect of the present invention is to provide a thin-filmmagnetoresistive sensor element for detecting a magnetic field componentperpendicular to the substrate, wherein this sensing element includes afree layer, a reference layer, and a spacer layer located between thefreelayer and the reference layer. The easy axis of the freelayerferromagnetic material is perpendicular to the plane of the substrate,but the direction of magnetization of the reference layer is constrainedto a direction parallel to the substrate plane, by the use of shapeanisotropy. The ferromagnetic material, the reference layer may have ahigher coercivity than the freelayer ferromagnetic material, and thespacer layer is made of an insulating or electrically conductivematerial is made.

The fifth aspect of the present invention is to provide a combination ofsaid sensing elements, deposited onto the same substrate, and formedinto a plurality of shapes, such that each sensing element inclinedalong one of two or more axes with respect to the applied magneticfield, thereby producing an array of sensors or differing sensitivity.

A sixth aspect of the present invention is to combine said sensingelements to an electronic device used for the deconvolution of thevarying response of the plurality of sensing elements into two or threeorthogonal magnetic field components.

The seventh aspect of the present invention is to provide a thin-filmmagnetoresistive sensor element for detecting a magnetic field componentperpendicular to the substrate, the sensing element includes a freelayer, a first reference layer, an insulating layer disposed betweensaid reference and free layers, a second reference layer, a secondspacer layer located between the free layer and the second referencelayer. The inherent easy axis of the freelayer material is perpendicularto the substrate; the magnetization direction of the first referencelayer is limited to a direction parallel to the plane of the substrate,the first reference layer is composed of a ferromagnetic material havingperpendicular anisotropy and shape anisotropy, the first reference layerhas a higher coercivity than the freelayer; the direction of themagnetization of the second reference layer is opposite to themagnetization direction of the first reference layer; the secondreference layer is composed of a ferromagnetic material withperpendicular anisotropy and shape anisotropy, and it has a highercoercivity than the freelayer; The first spacer layer made of aninsulating material; the second spacer layer is made of a conductivematerial.

The eighth aspect of the present invention is to combine said sensingelements to an electronic device used for the deconvolution of thevarying response of the plurality of sensing elements into two or threeorthogonal magnetic field components.

A ninth aspect of the present invention is to combine said sensingelements to an electronic device used for the deconvolution of thevarying response of the plurality of sensing elements into two or threeorthogonal magnetic field components.

The present invention also provides several combinations of sensingelement composition and arrays, wherein the arrays of sensor elementsare deposited onto the same substrate and arranged around the highpermeability ferromagnetic plate in different positions in order todecompose the applied magnetic field into different directions. Thepresent invention correspondingly provides several electronic devicescoupled with a combination of these sensing elements in order todeconvolute the response of the sensor arrays into a measure of the treeorthogonal components of the applied magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—Geometry of the sensor film showing the coordinate system.

FIG. 2—Schematic drawing of an exemplary MTJ field sensor materiallayering sequence in which a permanent magnetic is used to control thecharacteristics of the sensor response. Here the PL magnetization isfixed perpendicular to the plane of the film, and the FL is free to movebetween the perpendicular and parallel directions. With this orientationof the PL magnetization, the sensor detects the out-of-plane componentof the FL magnetization. A second PL may be added with magnetizationoriented to control the centering of the resistance as a function ofapplied magnetic field curve.

FIG. 3—A plot showing the effect of parallel fields on resistance of theperpendicular anisotropy MTJ device.

FIG. 4—A schematic drawing of a layout for a multi-axis sensor composedof several perpendicular anisotropy MTJ sensor elements of varyingshapes.

FIG. 5—A schematic drawing of a layout for a multi-axis sensor composedof several perpendicular anisotropy MTJ sensor elements. Sensors arearranged around a permeable ferromagnetic plate in order to separate theapplied magnetic field into three different components.

FIG. 6—Illustration of manner in which magnetic poles form around asquare plate in an applied magnetic field.

FIG. 7—Method by which in-plane magnetic fields are transformed intoperpendicular magnetic fields near the induced magnetic poles of theconcentrator. The schematic is across section of the concentration alongthe applied field direction.

FIG. 8—A schematic drawing of an electronic system used to transform theresponse of the sensor system into three orthogonal components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 defines the coordinate system of the vector magnetometer (VM,vector magnetometer). Here a magnetic sensor is deposited on a substrate5 that lies in the XY plane. The X and Y coordinates are referred to asin-plane or parallel to the plane of the substrate directions, and theZ-axis represents the perpendicular to the surface of the substratedirection.

The preferred sensor for application in the present invention is an MTJsensor that has been designed to be responsive to magnetic fieldsapplied in the Z-direction. Generally, MJ sensors are composed of aminimum of three important layers, which can be referred to as the freelayer (FL), the pinned layer (PL), and a tunnel barrier. The FL and PLare composed of ferromagnetic alloys of various elements, including butnot limited to Ni, Fe, Co, Al, B, Mo, Hf, Pd, Pt, and Cu. Themagnetization of the PL is rigidly held in place and does not varysignificantly in response to an applied magnetic field, and themagnetization of the FL is free to orient in response to an appliedmagnetic field. The tunnel barrier is an insulating material is usuallyan oxide, such as AlO_(x) or MgO.

MTJ devices exhibit a change in resistance as measured between the PLand FL that is related to the relative orientation of the FL'smagnetization direction with respect to the PL's magnetizationdirection. This is known as tunneling magnetoresistance (TMR). Thechange in resistance is quantified by a parameter referred to as the TMRratio.

$\begin{matrix}{{T\; M\; R\mspace{14mu}{Ratio}} = \frac{R_{AP} - R_{P}}{R_{P}}} & (1)\end{matrix}$

Here R_(AP) is the resistance of the MTJ when the magnetization of theFL and PL are aligned antiparallel to each other, and R_(P) is theresistance measured when the magnetization of the FL and PL layers isparallel. Generally, R_(AP) is greater than R_(P), and the resistancevaries as the cosine of the angle between the magnetization of the PLand FL layers.

A schematic drawing of the preferred sequence of layers in a MTJ deviceis shown in FIG. 2. The preferred device has an FL 30 that has a PLlocated adjacent to it on both sides. The top and bottom PLs, PL1 11 andPL 10, have their magnetization set in opposite orientations for thepurpose of cancelling stray field produced by the PL layers on the FLlayer that might cause asymmetry in the magnetic response of the MTJdevice. In order to make the MTJ device responsive to magnetization inthe Z-direction, the PLs are magnetized along the Z-axis, andadditionally, the spacer layers 20, 21 separating the PLs from the FL30, are composed of different materials. In the preferred embodiment,one spacer layer 20 is composed of MgO, and the other 21 is composed ofCu. MgO generally exhibits a much larger MR Ratio than devices builtusing a Cu spacer layer, so the change in resistance of the MTJ devicereflects the relative magnetization angular difference between the PL 10and FL 20. If the spacers were both composed of the same material, theincrease in resistance across one spacer layer would compensate thedecrease across the other, and the net magnetoresistance of the MTJsensor device would be very small. The PM layers 80 are used to providea magnetic bias on the FL 30 that reduces hysteresis and linearizes theresponse of the MR of the device to an applied magnetic field by helpingto keep the FL 30 free of magnetic domains.

The resistive response of the MTJ device to an applied magnetic field isshown in FIG. 3. The horizontal axis of the plot represents magnitude ofthe magnetic field applied along the Z-axis. The vertical axisrepresents the tunnel magnetoresistance across the insulating spacerlayer. Curve 74 shows the expected variation of the resistance whenthere is no field applied in the XY plane. Line 75 shows the effect ofapplying a field in the XY plane, which is to decrease the slope of thelinear region of the R(H_(z)) curve. This cross-axis sensitivity is afunction of device geometry and materials. It may be increased ordecreased to some extent to suit the sensor design requirements.

The magnetization of the FL 30 generally prefers to orient parallel to adirection that is called the magnetic easy-axis. The orientation of thisaxis is dependent on magnetic anisotropy, which has contributions due tointrinsic anisotropy of the ferromagnetic materials K_(i), and shapeanisotropy, K_(s), which as the name of the term implies, is related tothe geometry of the FL layer. The total anisotropy of the FL is equal tothe sum of the intrinsic and shape contributions:K=K _(i) +K _(s)  (2)

There are other sources of magnetic anisotropy that could be used toadvantage in this device, including surface and stress anisotropy, butfor simplicity of the discussion, they will be ignored. The K valuevaries with orientation of the FL magnetization, and the easy axis isthe axis along which K is a minimum.

K_(s) is small when the magnetization is oriented along the longestdirections of the FL, thus the magnetization of the FL due to K_(s)would be expected to lie in the XY plane in the absence of large fieldsalong the Z-axis. If the FL is patterned into an ellipse, themagnetization would be expected to lie along the long axis of the FL inthe XY plane.

In order to make the magnetization prefer to align out of plane, K_(i)needs to have a large in-plane value that compensates the out of planeK_(s). This results in an easy-axis that is in the out of planedirection, it is thus often referred to as perpendicular anisotropy.Alloys containing Ni, Co, Fe, Pt, Pd, and Tb are often used to producethis perpendicular anisotropy in thin films. Binary allows such as CoPt,FePt, and CoPd are the most commonly used. It is also possible to inducea surface anisotropy that favors magnetization alignment perpendicularto the surface of the FL, and this has been accomplished in very thinfilms of CoFeB with various capping layers, such as Ta.

For linear operation as a magnetic field sensor, it is preferred to haveK_(i) slightly less than K_(s), so that the FL magnetization prefers toalign in plane, but moderate values of a magnetic field applied alongthe out of plane direction, H_(z), can cause the magnetization to rotateout of plane.

Using perpendicular anisotropy materials and by varying the shape of thesensors, it is possible to make different sensors on the same substratethat respond to different components of the applied field. If the PLmagnetization is set in the XY plane, then the MTJ will be sensitive toFL magnetization components parallel to the XY plane. As the FLmagnetization is rotated out of plane by H_(z), the resistanceapproaches an intermediate value. As it rotates in plane parallel oranti-parallel to the PL magnetizations direction, the resistanceapproaches a minimum or a maximum.

Alternatively, if the PL magnetization is set in the Z direction, thenthe sensor will be most strongly sensitive to FL magnetizationcomponents along the Z-axis. Additionally, the shape of the FL can beused to make the magnetization rotate more in response to a field alongone in-plane axis, say the X-axis, than another axis, say the Y-axis.This effect can be used to cause the sensor to be more responsive tomagnetic fields applied along one in-plane axis than another. Finally,the sensor can be designed so that it is round or biased in such a wayusing a permanent magnetic so that it is equally sensitive to fieldsapplied in the XY plane, but most strongly responsive to fields appliedalong the Z-axis.

In any case, it is apparent that using the same sensor film deposited ona substrate, it is possible to pattern neighboring MTJ sensors intoshapes that have different response to the different components of anapplied magnetic field. This feature can be used to build a single chipvector magnetometer. A schematic drawing of a single chip magnetometerconcept is shown in FIG. 4. Here three different sensor shapes each ofwhich responds most strongly to one of the three preferred components ofthe applied magnetic field are patterned into the MTJ film. One sensor90 is most sensitive to magnetic fields applied along axis 1 and anothersensor 91 is more sensitive to magnetic fields applied along axis 2. Amagnetic field is applied using permanent magnets 80 to bias thein-plane sensors 90 and 91 for low hysteresis operation, and tocompensate the Z-sensor 92 so that it is equally responsive to magneticfields applied in the XY plane.

FIG. 5 illustrates another design concept for building a vectormagnetometer using perpendicular anisotropy in MTJ devices. In thiscase, the sensor includes a square high permeability ferromagnetic plate220, which disturbs the applied magnetic field and changes the directionof the applied magnetic field near the edges of the plate. This isbecause the permeable concentrator 220 magnetically polarizes inresponse to the applied field and at least in a mathematical descriptionof the problem, forms the equivalent of magnetic poles at the ends ofthe plate where the magnetic field enters and leaves the plate as shownin FIG. 6. The strength of the magnetic poles is linearly proportionalto the applied in-plane magnetic field. FIG. 7 shows a XZ cross-sectionof the permeable concentrator 220 when a field is applied along the Xdirection. Note that the applied field is steered in the upwarddirection on the left-hand side of permeable concentrator 220, anddownward on the right-hand side of permeable concentrator 220. Z-axismagnetic field sensors placed at the left and right hand sides of thepermeable concentrator will thus show opposite changes in resistance tofields applied in plane. The difference between the resistance values ofthe two sensors at opposite sides of the permeable concentrator 220 isthus indicative of the x-axis field, and it should be insensitive tofields applied along the Z and Y directions. Thus the configuration ofsensor shown in FIG. 5 should be useful for isolating differentcomponents of the applied magnetic field.

Neither vector magnetometer concept illustrated in FIGS. 4 and 5 areexpected to perfectly isolate the different magnetic field components,and there will be cross-axis sensitivity in each of the differentsensors to components that are not along the intended sensitivity axis.In order to resolve this problem, and also to overcome anynon-orthogonality between the sensitivity axes, a sensor system such asdepicted in FIG. 8 can be constructed.

The operating principle for the vector magnetometer system involvestreating the voltage output from each of different sensors as a sum ofthree polynomials of the different field directions H_(x), H_(y), andH_(z) along with a DC offset voltage. The following form is suggested:V ₁ −V ₁ ^(off) =C ₁₁ ^(x) H _(x) +C ₁₁ ^(y) H _(y) +C ₁₁ ^(z) H _(z) +C₁₂ ^(x) H _(x) ² +C ₁₂ ^(y) H _(y) ² +C ₁₂ ^(z) H _(z) ²+  (3)

The entire system of equations is then

$\begin{matrix}{{{V_{i} - V_{i}^{off}} = {\sum\limits_{j = 1}^{N}{\sum\limits_{k = x}^{z}{C_{ij}^{k}H_{k}^{j}}}}}\mspace{40mu}\ldots{{V_{M} - V_{M}^{off}} = {\sum\limits_{j = 1}^{N}{\sum\limits_{k = x}^{z}{C_{Mj}^{k}{H_{k}^{j}.}}}}}} & (4)\end{matrix}$

Here ‘M’ is the number of sensors in the array, and ‘N’ represents thenumber of terms used in the polynomial to fit the sensor response. Thesystem can be represented as a matrix equation.V−V ^(off) =C H  (5)

The equation can be inverted to find the H matrix, the desiredcomponents of the applied field.H=C ⁻¹(V−V ^(off))  (6)

For simplicity, consider a two axis sensor designed to detect H_(x) andH_(y). Assuming linear response, the outputs of the two sensors requiredfor the system would be described as follows:V ₁ −V ₁ ^(off) =C ₁₁ ^(x) H _(x) +C ₁₁ ^(y) H _(y)  (7A)V ₂ −V ₂ ^(off) =C ₂₁ ^(x) H _(x) +C ₂₁ ^(y) H _(y)  (7B)

As a matrix this is

$\begin{matrix}{\begin{pmatrix}{V_{1} - V_{1}^{off}} \\{V_{2} - V_{2}^{off}}\end{pmatrix} = {\begin{pmatrix}C_{11}^{x} & C_{11}^{y} \\C_{21}^{x} & C_{21}^{y}\end{pmatrix}\begin{pmatrix}H_{x} \\H_{y}\end{pmatrix}}} & (8)\end{matrix}$

The solution for H is then given as

$\begin{matrix}{\begin{pmatrix}H_{x} \\H_{y}\end{pmatrix} = {\begin{pmatrix}C_{21}^{x} & {- C_{11}^{y}} \\{- C_{21}^{x}} & C_{11}^{y}\end{pmatrix}\begin{pmatrix}{V_{1} - V_{1}^{off}} \\{V_{2} - V_{2}^{off}}\end{pmatrix}}} & (9)\end{matrix}$

Equation 9 could easily be solved by an on-chip microcontroller usingstored values of the C and V^(off) coefficients. The C and V^(off)matrix components can be determined by placing the sensor array in acalibration fixture and measuring V(H_(x),H_(y)) for each sensor atsufficient number of (H_(x),H_(y)) points in order to fit the responseto equation 7.

If the sensor response in also nonlinear in addition to showingcross-axis response, then higher order terms in the polynomial can beretained, but for each term retained, the number of sensors used in thearray must be doubled. If for example, it is necessary to include H³ inthe fit polynomial for the sensors, then the following system needs tobe inverted to find the field components of a two axis-sensor:

$\begin{matrix}{\begin{pmatrix}{V_{1} - V_{1}^{off}} \\{V_{2} - V_{2}^{off}} \\{V_{3} - V_{3}^{off}} \\{V_{4} - V_{4}^{off}}\end{pmatrix} = {\begin{pmatrix}C_{11}^{x} & C_{11}^{y} & C_{13}^{x} & C_{13}^{y} \\C_{21}^{x} & C_{21}^{y} & C_{23}^{x} & C_{23}^{y} \\C_{31}^{x} & C_{31}^{y} & C_{33}^{x} & C_{33}^{y} \\C_{41}^{x} & C_{41}^{y} & C_{43}^{x} & C_{43}^{y}\end{pmatrix}\begin{pmatrix}H_{x} \\\begin{matrix}H_{y} \\H_{x}^{3} \\G_{y}^{3}\end{matrix}\end{pmatrix}}} & (10)\end{matrix}$

Then in this case, 20 parameters will need to be stored for invertingthe equation. By analogy, the equation can be extended to include up tothree orthogonal axes and as many polynomial terms as can be practicallystored on chip. The minimum size of the storage area on chip is thenMemSize=Axes^(N)(Axes^(N)+1).  (11)

Where again, N is the number of terms used in the polynomial for each Hcomponent.

A representative on-chip computation system for inverting the systemequation for an array of sensors and mapping the voltage output from thearray of sensors into orthogonal magnetic field components is shown inFIG. 8. Here, the array of M sensors 100 is periodically selected andsampled using an analog multiplexer 110 and analog to digital converter(ADC) 120. The output from the ADC is fed into a microcontroller 130that is used compute the magnetic field values from the array of voltagevalues. The microcontroller uses calibration data that is stored inon-chip memory 150. The microcontroller provides output in digitalformat 140. The system may be designed so that it is calibrated at waferlevel, and so it can be recalibrated by the end-user through a specialcalibration mode.

It will be apparent to those skilled in the art that variousmodifications can be made to the proposed invention without departingfrom the scope or spirit of the invention. Further, it is intended thatthe present invention disclosure cover modifications and variations ofthe proposed invention provided that such modifications and variationscome within the scope of the appended claims and their equivalence.

What is claimed is:
 1. A thin-film magnetoresistive sensor element fordetecting a magnetic field component perpendicular to a plane of asubstrate of its deposition, comprising: a ferromagnetic free layer inwhich an intrinsic easy axis of a material of the ferromagnetic freelayer is set perpendicular to the plane of the substrate onto which theferromagnetic free layer is deposited, a ferromagnetic reference layer,wherein magnetization of the ferromagnetic reference layer isconstrained to lie perpendicular to the plane of the substrate, Whereinthe ferromagnetic reference layer comprising a ferromagnetic materialwith perpendicular anisotropy and shape such that the ferromagneticreference layer has a higher coercivity than the ferromagnetic freelayer, a spacer layer between said ferromagnetic free layer andferromagnetic reference layer, wherein the space layer, comprisingeither an insulating or a conducting material, an electronic systemcoupled to the array of the sensor element to be used to deconvoluteresponse of the array of the sensor element into a coordinate systemdescribing two or three orthogonal magnetic field directions, andwherein each sensor element is deposited on the same substrate, andpatterned into a collection of shapes, each of which has a differentsensitivity to magnetic fields applied along two or more oblique axes.2. A thin-film magnetoresistive sensor element as in claim 1, comprisingpermanent magnets disposed such that they apply a magnetic fieldparallel to the ferromagnetic free layer in the direction parallel tothe plane of the substrate, wherein said magnetic field is applied inorder to reduce hysteresis of response of the ferromagnetic free layerto fields applied perpendicular to the plane of the substrate.
 3. Athin-film magnetoresistive sensor element for detecting a magnetic fieldcomponent perpendicular to a plane of a substrate of its deposition,comprising: a ferromagnetic free layer in which the intrinsic easy axisof a material of the ferromagnetic free layer is set perpendicular tothe plane of the substrate onto which it is deposited, a firstferromagnetic reference layer in which the magnetization of the firstferromagnetic reference layer is constrained to lie perpendicular to theplane of the substrate, wherein the first ferromagnetic reference layercomprising a ferromagnetic material with perpendicular anisotropy andshape such that the first ferromagnetic reference layer has a highercoercivity than the ferromagnetic free layer, a spacer layer betweensaid ferromagnetic free layer and the first ferromagnetic referencelayer, comprising an insulating material, a second reference layer withmagnetization oriented in a direction opposite to that of the firstferromagnetic reference layer, wherein the second reference layercomprising a ferromagnetic material with perpendicular anisotropy andshape such that the second reference layer has a higher coercivity thanthe free layer, a spacer layer between the ferromagnetic free layer andthe second reference layer, comprising a conducting material, anelectronic system coupled to the array of the sensor element to be usedto deconvolute response of the array of the sensor element into acoordinate system describing two or three orthogonal magnetic fielddirections, and wherein each sensor element is deposited on the samesubstrate, and patterned into a collection of shapes, each of which hasa different sensitivity to magnetic fields applied along two or moreoblique axes.
 4. A thin-film magnetoresistive sensor element as in claim3, comprising permanent magnets disposed such that they apply a magneticfield parallel to the ferromagnetic free layer in the direction parallelto the plane of the substrate; said magnetic field is applied in orderto reduce hysteresis of the response of the ferromagnetic free layer tofields applied perpendicular to the plane of the substrate.
 5. An arrayof the sensor element as in claim 1, wherein each sensor element isdeposited on the same substrate, and arranged in various positionsaround a permeable ferromagnetic plate in order to separate an appliedmagnetic field into different components.
 6. An array of the sensorelement as in claim 5, wherein an electronic device is coupled to thearray of sensor element to be used to deconvolute the response of thevarious sensor elements into a coordinate system with three orthogonaldirections.
 7. An array of the sensor element as claimed in claim 3,wherein each sensor element is deposited onto the same substrate andarranged in different positions around a circumference of a highmagnetic permeability ferromagnetic plate in order to separate anapplied magnetic field into different components.
 8. An array of thesensor elements as claimed in claim 7, wherein the array of the sensorelement are connected to an electronic apparatus that is used todeconvolute the response of the various sensor elements into threeorthogonal coordinates.